This invention relates to a novel rotary microtome with a crank mechanism.
A rotary microtome generally includes an object carriage. The object carriage carries a specimen holder that holds a specimen to be cut. The object carriage is moved up and down in a vertical path on the rotary microtome. During this vertical movement, the specimen is passed over a cutter fixedly arranged on the rotary microtome.
In conventional rotary microtomes, control of the vertical cutting movement generally takes place by means of a crank mechanism which is driven by a handwheel. The crank mechanism transforms turning movement of the handwheel into vertical movement of the object carriage. In this type of drive, the moveable masses of the rotary microtome, which includes the specimen and all of the moveable components of the microtome, are alternately and repeatedly accelerated and decelerated. Gravitation accelerates the moveable masses during a first half-turn of the handwheel (downward movement of the object carriage) and decelerates the moveable masses during the second half-turn of the handwheel (upward movement of the object carriage). Thus, only a force reduced by the force of gravitation is required on the handwheel during the downward movement of the object carriage, and a force increased by the force of gravitation is required during the upward movement.
To balance these undesired accelerations and decelerations, rotary microtomes include mass-balancing means. The mass-balancing means generally comprises an asymmetrical balancing weight which is integrated into the handwheel.
Where the moveable masses of the rotary microtome are relatively large, the balancing weight must be dimensioned to be correspondingly large, thereby increasing the bulk of the microtome. Furthermore, an asymmetrically formed balancing weight may produce undesirable vibrations in the rotary microtome during relatively fast upward and downward movements of the object carriage. Vibrations in the microtome inevitably lead to specimens which are uneven and consequently cut in such a way that they are unusable.
DE 33 47 238 C1A discloses a means for dispensing with an asymmetrically formed mass integrated into the handwheel. This document describes a mass-balancing Means which has a cam element fastened on the drive shaft of a crank mechanism. A pivotably mounted lever is positioned on the cam element. A spring element produces the compressive force of the pivotably mounted lever. The torque produced by the lever is dependent on the respective position of the cam element. The torque produced by the lever is inversely proportional to the torque of the microtome's moveable masses at every position of the crank mechanism. Consequently, the handwheel can be actuated uniformly over its entire turning angle.
It has been found in practice, however, that, here too, the microtome vibrates. The cam element causes vibrations during relatively fast cutting movements so that smooth and even cuts can be produced only at a relatively slow drive speed.
The difficulties suggested in the preceding are not intended to be exhaustive but rather are among many which and to reduce the effectiveness of prior rotary microtomes. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that such apparatuses appearing in the past will admit to worthwhile improvement.
Accordingly, it is therefore a general objective of the invention to provide a rotary microtome which will obviate or minimize difficulties of the type previously described.
It is a specific object of the invention to provide a rotary microtome having a microtome drive that produces no vibrations in the microtome, even at relatively high drive speeds or cutting speeds.